Results of studies on the predictive value of plasma concentrations of Aβ40 and 42 amyloid peptides for incident AD are not straightforward. Discrepancies in these results may be due to the fact that total peptide concentrations have been measured. One recent study suggests that plasma free Aβ peptide concentration and particularly low-density lipoprotein receptor-related protein (LPR) as like as free Aβ/total Aβ ratio would be more reliable and discriminant.